The static pushover analysis (SPA) procedure has been widely applied to the estimate of the nonlinear seismic performance of the multistory structure subjected to horizontal earthquakes. However, SPA could hardly obtain a satisfying result in accuracy when applied to the evaluation of seismic responses of the largespan latticed arch under vertical earthquake ground motions, whose lateral and vertical displacements were coupled. Accordingly, an improved modal pushover analysis (IMPA) procedure was proposed, based on the eigenstiffness, introduced from the static stability analysis of structures. Firstly, equivalent single degree of freedom (ESDOF) system was established based on eigenstiffness by modal pushover analysis for each mode selected. Secondly, the seismic responses of the ESDOFs were solved respectively and combined. Finally, the seismic responses of the structure were obtained by pushover analysis once more according to the load formula derived. The seismic responses of a latticed arch under a series of vertical earthquake waves on firm and soft sites, were obtained by IMPA. Compared with the results given by response history analysis, the node vertical displacements and the most unfavorable stresses of the arch were consistent in distribution, with errors about 10.5% and 33.2% respectively, and 25% computing consumption. Along with the increase in the number of the vertical modes selected of the arch, the accuracy of IMPA could improve.